This is the absolute last day you can file your 2015 taxes

Ask almost any American citizen when tax day is, and you're likely to hear "April 15th". While this is normally the day that taxes are due, that isn't the case this year. With that in mind, here are the "Big Three" dates to remember this year.

April 18, 2016
No, April 15 doesn't fall on a weekend this year. So why do your taxes need to be filed -- and your outstanding balance paid -- three days latet this year? Because in Washington, DC -- and DC only -- April 15th is a holiday this year: Emancipation Day.

This celebrates the day that Abraham Lincoln signed the Compensated Emancipation Act, which freed over 3,000 slaves living in the District of Colombia, well before the universally known Emancipation Proclamation was signed. Usually this falls on April 16, the day Lincoln signed the Act. But that falls on a Saturday this year, and by law, it needs to be celebrated on the nearest weekday.

Not only should you file and pay for any outstanding balance on your taxes, but if you need an extension, you must file Form 4868 before April 18.

October 17, 2016
If you were able to file for your extension in time, this is the new date by which you must file your taxes and pay any outstanding balances. Like the "normal" tax day, this usually falls on October 15, but because that is a Saturday this year, October 17 is the new date.

April 15, 2019
Double-check that year again so you understand what we're talking about here. It's not a misprint: it's supposed to say "2019." If you go back and read over the two previous dates, you'll see that I wrote "pay for any outstanding balance." That's because if you're actually owed a refund, the Treasury gives you three more years to file your taxes in order to claim it.

Of course, the Department has good reason for doing this: by waiting three years to claim your refund, you are giving the government an interest-free loan over a very long time period. But be careful, waiting this long will only work in your favor if you are certain that you'll be owed a refund. If you calculated wrong, the penalties for being three years late can be very hefty -- and this situation should be avoided in general if you want to stay out of hot water.

Don't forget: a refund isn't necessarily a "good" thing
With this year's tax date less than one month away, and the current tax year almost one-quarter finished, it's good to remind readers that a refund isn't as great as it might make you feel. In the end, it means that more money was taken out of your regular paycheck than needed to be. As a result, you missed the opportunity to invest whatever that difference is. Compounded over your entire working life, this could make a big difference in your retirement savings.

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Related: Tips on how to avoid a tax audit:

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This is the absolute last day you can file your 2015 taxes

Double check your figures to assure there are no mistakes

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Be sure to be 100% honest, and report your numbers realistically

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Those in the highest and lowest income brackets are most often targets of fraud, and thus, audits